Preparation of cellulose xanthate solutions



Patented Apn- 13, 1937 UNITED STATES PREPARATION OF CELLULOSE XANTHATE SOLUTIONS George A. Richter, Berlin, N. H.,.assignor to Brown Company, Berlin, N. 11., a corporation of No Drawing. Application July 8, 1933, Serial No. 679,585. Renewed March 20, 1936 11 Claims. (Cl. 260-100) This invention relates to the preparation of cellulose xanthate solutions or viscose syrups such as are used in various industries, including the manufacture of viscose silk so-called and pelliclesof regenerated cellulose, the sizing or coating of paper and textile fabrics, etcs In previous patents,'I have disclosedthe advantages ensuing from the reduction of cellulose fiber before it is converted into various cellulose derivatives and more particularly into cellulose xanthate. Thus, in my Patent No.' 1,842,689, dated January 26, 1932, I have pointedout the value of mechanically reducing cellulose. fiber to a powdered condition prior to xanthation, and have further pointed out that little, if any, ageing of the reduced cellulose need be performed to give rise to a ready and substantially combe much less than that causing mercerization 0 at the particular temperature at which the mixture is employed. Such practice is highly advantageous in that it takes only two steps to prepare a xanthate solution, whereas the usual practice involves many more steps, namely, those of sheeting the cellulose fiber, of soaking the sheets in a mercerizing caustic soda solution, of squeezing the sheets free of excess solution, of disintegrating the sheets of soda cellulose into a fluffy mass, of ageing the mass of soda cellulose, of xanthating the aged soda cellulose, and of dissolving the xanthate in a dilute caustic soda solution.

In preparing a conventional kind of viscose syrup containing in solution approximately7% caustic soda and 7% cellulose in the form of xanthate, the practice accordant with the present invention may be substantially as follows. Suitable chemical wood pulp, such as bleached sulphite pulp or bleached, refined sulphite or other wood pulp of high alpha cellulose content, is put through a suitable pulverizing ma-.

chine, e. g., a ball or roller mill, and the resulting powdered cellulose sifted through a fine screen, preferably a ZOO-mesh sieve, but coarser screens, flax; a IOU-mesh screen, may be used, although with some sacrifice in the rate of the subsequent xanthating reaction; The resulting powdered cellulose is then commingled with an amount 'of water, caustic soda, and carbon bisulphide mentioned. It is found that under normal room temperature conditions and with stirring of the mixture, the powdered cellulose progres-.

sively'goes into solution to form a clear, sparkling solution of cellulose xanthate substantially devoid of residual or unreacted cellulose particles.

The manufacture from viscose of various-endproducts is accomplished most satisfactorily with viscose syrups of low viscosity such as owe their low viscosity characteristic to the particular kind of cellulose from which they have been prepared. In such instances, therefore, it is desirable. to select as the starting fiber to undergo mechanical pulverization chemical wood pulp or the like of low solution viscosity. I have taken out a number of patents disclosing processes of lowering the solution viscosity of chemical wood pulp or the like. Of these patents, Patent No. 1,906,885, dated May 2, 1933, which discloses the refinement of chemical wood pulp. and more particularly sulphite pulp in a mercerizing liquor followed by bleaching, may be cited as an illustration, as the resulting cellulose fiber is of low solution viscosity and has high reactivity toward the'usual xanthating reagents. The cellulose powder derived from chemical wood pulp or the like having low solution viscosity, say, a viscosity of less than 2 (3.6. S. units in a standard cuprammonium solution, as disclosed in that patent, is advantageous not only because it yields xanthat'c solutions of high fluidity but because it tends to react comparatively quickly with the single reacting mixture of the present invention containing both caustic soda andcarbon bisulphide. despite the fact that the reaction mixture is of much lower than mercerizing strength and no recourse is had to cooling of the mixture for the purpose of promoting the reaction.

It might be pointed out that ordinary chemical wood pulp, such as the sulphite pulp, heretofore used in the viscose-making industry, cannot be successfully xanthated in its usual unreduced fibrous condition in xanthating reagents such as are applied in the practice of my invention. It might be reasoned that a xanthating mixture, whose 'causticity is comparable to the 18% caustic soda solution used in the standard practice of making viscose, would do the worlnbut I havefound it practically impossible to mix an 18% caustic soda solution with pulp in amount designed to yield a xanthate solution of 18% cellulose content so that the xanthate such conditions so as to conduce to the desired solution might be diluted with water to yield a typical solution, for instance, one of 7% cansticity and 7% cellulose content, such as is desired for spinning into artificial silk or for casting into pellicles of regenerated cellulose. Indeed, aside from the difllculty of stirring or mixing the pulp with the xanthating reagents under The cellulose used as raw material in the process'oi the present invention maybe derived from various sources. Indeed, when; such factorsas color and purity are-of no particular moment in the end-products into. which the viscose enters, the'raw material. tobe: subjected to'the initial step of pulverization may be waste papers, cotton and linen rags; flax, wdod, or other waste or raw forms of cellulose associated with considerable natural impurities such as lignin, resin,

etc., or extraneous impurities-suchas the sizes,

fillers, and pigments used in paper or textile fabric manufacture. In the case of such more expensive end-products as artificial and films wherein such qualities as lightness of color, transparency, maximum luster and strength, etc., are

0' prized, the raw material should be of adequate purity as typified by chemical wood pulps, such as bleached sulphite pulp, and more especially cotton or chemical wood pulps refined to'an alphacellulose content, say, 93% to 98% and possessed 45 of high whiteness. In the case of some forms of raw material that have undergone a particular mechanical or chemical treatment-rendering such material ,unfit for the usual viscose-making process, it becomes possible by my invention to proso duce therefrom viscose solutions possessed of dey sirable qualities, such as low. viscosity. Glassine paper, parchment paper, and vulcanized papers ,or boards, which represent cellulose fiber in a highly hydrated condition by virtue of the mechanical or chemical treatment applied thereto,

fall into this category of raw material. 'When such raw material is processed in the usual manner, it is impossible to produce viscose solutions of suitable clarity, for not only is such material quite dense and resistant to penetration by caustic soda solution, but it fails to disintegrate and fiufi up satisfactorily. The characteristics of such raw material are, however, nowise disturbing to the process of the present invention. On thecontrary, such qualities as density, hardness, and brittleness, lead to readv mechanical pulverization and, when the raw material has been subjected to such previous chemical treatmentas parchmentization with strong sulphuric acid solution, the xanthate solution prepared therefrom by the practice of my invention may have. aviscosity as low as that of a xanthate solution prepared from aged soda cellulose in the conventional way.

In the case of some kinds of rawmaterial, the

16 process of the present inventionisadvantageous in that it leads to substantially complete xanthation when the conventional viscose-making process does not, for instance, virgin cotton, bleached kraft pulps, and chemical wood pulps derived fromv deciduous woods and even refined to high alpha cellulose content, ,resist xanthation as conventionally practiced. In such case, although most of the raw material is reacted upon, there is a sufllcient residue to render the xanthate solution unsatisfactory for use in the manufacture of I artificial silk and transparent sheet material. I have found, however, that when such raw materials are first pulverized or sub-divided, probably by virtue of their increased surface and the rupture of resistant material such as resins which partially or completely envelop the fibers, I- can obtain clear xanthate solutions by the single-step xanthate reaction of the present invention, even though the caustic soda solution is used in the tional viscose-making process. Such short-fibered pulp sheets have insufilcient strength to permit transfer in an intact condition from the press to the grinder; and it is usual to find that fragments break 01! from the sheets into the solution and greatly impair the subsequent impregnating efficiency of the solution especially after a few uses. Again, it has been my observation that short-fibered, hardwood pulps do not tend to xanthate uniformly when subjected in the form of soda cellulose to the action of carbon bisulphide. Apparently, the grinding action to which the sheets of hardwood pulp are subjected after being steeped in the caustic soda solution and pressed does not satisfactorily break apart or separate the fibers. doubtless on account of their short average fiber length. In other words hard fiber clumps or pasty pellets are in'such case inevitably introduced into the xanthating drums and resist penetration by the carbon bisulphide vapors introduced into the drums for the xanthating reaction. The foregoing troubles are avoided when powdered cellulose undergoes xanthati'on in accordance with my invention in a single bath containing both the caustic soda comesuspende d in the xanthating mixture in such a way as to permit of uniform and quick reaction. that together with the caustic soda and carbon bisulphide constituting the xanthating reagent, sufilcient water may be used to form a xanthate solution of the ultimate strength desired, al-

though in somecases dilution with water may be effected for the desired ultimate uses after the xanthating reaction has been completedwhen all the water desired in the finished xanthate -solution ,constitutes part of the xanthating mixturathere is a large excess of liquid vehicle in which the finely divided cellulose can be sus-' pended, wherefore smooth'reactionto-completion is readily attained.

In some instances, when the cellulose used as a starting is of; afnonhydratable character as typ ed by mercerized cellulose pulp, the cellulose fiber used as raw ma- Y terial may advantageously be reducedtoa puland the carbon bisulphide, as the particles be-' In this connectionpit is to be observed for instance. liquids like benzol, alcohol, or the like, which are volatile and which inhibit hydration of the fiber, assuming that the fiber is of a hydratable character and it is desired to inhibit or prevent hydration. In such case, the excess of non-aqueous liquid may, 1f desired, be removed from the powder and, if desired, any residue removed by volatilization. Part or all of the carbon bisulphide necessary for xanthation may, if desired, constitute the non-aqueous wetting medium in which pulverization of the fiber is accomplished, in which case, there need be no removal of the carbon bisulphide from the powder, inasmuch as the carbon bisulphide may enter into'the subsequent xanthating reaction. In powdering cellulose fiber in a wet way, for instance, in the presence of water as the wetting medium, not only is it'possible to use for such purpose impact machines of the class already mentioned, but sharp Jordans or similar machines through which the fiber may be passed a number of times until the desired subdivision thereof has been effected. The resulting wet powder or powder suspension need not necessarily be dried before the xanthating reaction but may, as already indicated, he used in the form of an aqueous slurry and treated in accordance with my invention with an amount of car-' conditions, through an orifice of standard size The solution viscosity of fiber is hereinbefore given in absolute C. G. 8. units or noises. 50 I claim:

1. In the manufacture of cellulose xanthate, those steps which comprise .pulverizing cellulose to fine particle size, and then causing such pulverulent cellulose to react simultaneously with 55 carbon bisulphide and a. solution of alkali under non-mercerizing conditions of both alkalinity and temperature.

2. In the manufacture of cellulose xanthate, those steps which comprise pulverizing cellulose 60 to a particle size finer than about 200 mesh, and then causing such pulverulent cellulose to react simultaneously with carbon bisulphide and a solution of alkali under non-mercerizing conditions of both alkalinity and temperature.

3. In the manufacture of cellulose xanthate, that step which comprises causing mechanically powdered cellulose of fine particle size to react simultaneously with carbon bisulphide and a solution of caustic, soda under non-mercerizing 70 conditions of both alkalinity and temperature.

4. In the manufacture of cellulose xanthate,

ly with carbon bisulphide and with a solution of caustic soda under non-mercerizing conditions of both alkalinity and temperature in such proportions as to yield directly at xanthate solution of about 6% to 10% causticity and about 6% to 7% cellulose content. l

5. In the manufacture of cellulose xanthate, those steps which comprise mechanically pulverizing cellulose to a particle size finer than about 200 mesh, and then causing the powdered cellulose to react substantially to completion simultaneously with carbon bisulphide and a solution of caustic soda under non-mercerizing conditions of both alkalinity and temperature in such proportions as to yield directly a xanthate solution of about 6% to 10% causticity and about 6% to 7% cellulose content.

6. In the manufacture of cellulose xanthate,

those steps which comprise mechanically pulverizing cellulose of low solution viscosity to fine particle size, and then causing such cellulose to react substantially to completion simultaneously with carbon bisulphide and a solution of alkali under non-mercerizing conditions of both alkalinity and temperature.

7. In the manufacture ofcellulose xanthate, those steps which comprise chemically treating cellulose to reduce its solution viscosity to a value of less than -2 C. G.-S. units in a standard cuprammonium solution, reducing the treated cellulose to a particle size finer than about 200 mesh, and then causing such cellulose particles to react simultaneously with carbon bisulphide and a solution of alkali under non-mercerlzin'g conditions of both alkalinity and temperature.

8. 'In the manufacture of cellulose xanthate, those steps which comprise pulverizing cellulose to fine particle size in the presence of a wetting medium, and then causing such pulverulent cellulose to react simultaneously with carbon bisulphide and a solution of alkali under non-mercerizing conditions .of both alkalinity and temperature.

9. In the manufacture of cellulose xanthate, those steps which comprise pulverizing cellulose to fine particle size in the presence *of sufiicient water to form an aqueous slurry of powdered cellulose, and then treating the aqueous slurry with carbon bisulphide and caustic soda under non-mercerizing conditions of both alkalinity and temperature in such proportions and concentrations as to yield directly a xanthate solution of about 6% to 10% causticity and about 6% to 7% cellulose content.

10. In the manufacture of cellulose xanthate,

those steps which comprise reducing cellulose pulp to a particle size finer than about 200 mesh, and then causing such cellulose particles to react simultaneously with carbon bisulphide and a solution of caustic soda of about 7% strength at about room temperature.

11'. In the manufacture of cellulose xanthate, those steps which comprise reducing cellulose pulp to a particle size finer :than about 200 mesh, and then causing such cellulose particles toreact simultaneously with carbon bisulphide and a solution of-caustic soda of about 7% strength at about room temperature and 'insuch proportions as to yield directly a xanthate solution of about 7% causticity and about 7% cellulose content.

GEORGE A. RICHTER. 

